The present invention relates to an antenna assembly suitable for wireless transmission of analog and/or digital data, and more particularly to a combination of a microstrip patch and a bowtie slot antenna radiating element enabling operation at dual frequency bands and featuring high gain in each band
There exists a need for an improved antenna assembly that provides a single and/or dual band response and which can be readily incorporated into a small wireless communications device (WCD). Size restrictions continue to be imposed on the radio components used in products such as portable telephones, personal digital assistants, pagers, etc. For wireless communications devices requiring a dual band response the problem is further complicated. Positioning the antenna assembly within the WCD remains critical to the overall appearance and performance of the device.
Antenna assemblies compatible with printed circuit fabrication technologies are known and have found application in radar, satellite communication and other present day systems. In these antenna assemblies a conductive line or pattern realized in the form of printed circuit conductor is often used to communicate radio frequency energy to or from the antenna element.
One known antenna structure is the xe2x80x9cpatchxe2x80x9d antenna. Such antennas may consist of a printed circuit conductor area of selected and resonance-based physical size disposed at the terminal point or other selected node along a radio frequency conductor. The patch antenna is found to be with several limitations; the primary of which is a limited bandwidth capability. Patch antenna bandwidth often extends over only a few percent of the antenna""s design frequency and gives rise to difficulty in spread spectrum communications or multiple systems use applications of the antenna. The present invention in which the patch antenna is improved-upon by combining it with a selected additional form of bowtie slot antenna is believed to provide a desirable addition to the family of antennas usable with wireless communications devices.
The present invention provides a combination of a microstrip patch and a bowtie slot antenna radiating element enabling operation at dual frequency bands and featuring high gain (7-10 dBi) in each band. Additional features include excellent bandwidth (over 10%) for each band, and also enhanced performance and less pattern distortion as compared to either a typical patch or a typical bowtie slot antenna. The antenna device can be used for example, as a base station antenna, or micro cell, or access point site antenna, for wireless communication devices, such as cell phones, PDA""s, laptop computers, or other devices which can employ wireless communication antennae. Another particular advantage of the invention is the ability to serve both frequencies using a single common feed.
The antenna radiating element can be fabricated using known printed circuit board fabrication techniques and processes. In one embodiment, the antenna radiating element is provided on a single printed circuit board of a dielectric material with two major surfaces or sides. The printed circuit board has copper plating on one or both sides of the dielectric material. In operation, the antenna is disposed in relation to a corresponding ground plane. On the first side, which faces the ground plane, the bowtie shape is defined and may be selectively etched from the conductive surface of the board material. On the second side, optional conductive antenna pattern enhancement elements can be disposed. In alternative embodiments, the antenna device can also be implemented using other manufacturing methods employing conductive material over dielectric material, such as plating, vapor deposition or plasma deposition of conductive material over non-conductive material, or could also be built using two-shot molding with selective plating, or other manufacturing methods as will be known or developed by those skilled in the art.
In one preferred embodiment (as shown in the enclosed figures,) an antenna according to the present invention serves as a dual band base station antenna to cover two frequency bands, namely GSM (880-960) MHz and 3 G UMTS Radio band (1.92-2.17) GHz. In other particular embodiments the invention can be implemented by one of ordinary skill in the art without an undue amount of experimentation, by scaling the dimensions, to provide dual ISM bands (2.4 and 5.8 GHZ), or also built to operate at the two frequency bands of ISM (2.4 GHz) and UNII (5.3 GHz), or other useful combinations of frequency bands. In each case, the two bands are fed with a single feed line and can be operated singularly or simultaneously. In one embodiment, the invention can be employed as a dual band antenna in conjunction with a multiband radio, with diplexers or other methods know in the art, to separate the bands. In another embodiment, the antenna could be used for either of the single bands provided, and is switched easily from one of the frequency bands to the other without modifications.
The frequencies of operation for a particular antenna embodiment can be implemented as follows; the low frequency band is primarily determined by the dimension xe2x80x98Dxe2x80x99 of the patch antenna portion, as shown in FIG. 1, while the higher frequency band operating characteristics are primarily determined by the dimensions of the bowtie slot and the backside antenna pattern enhancement elements.
The invention can also be incorporated into an array of antenna structures to increase directivity and gain, and such an array of antenna elements can be integrated with a corporate feed network as illustrated in FIG. 6.
It is one object of the invention to provide a dual band antenna device with a single feedline.
It is a further object of the invention to provide a dual band antenna device with wide bandwith (on the order of 10%) for each frequency band.
It is a further object of the invention to provide a dual band antenna device with high gain in each band (on the order of 7-10 dBi).
It is a further object of the invention to provide a dual band antenna device where the two bands can be simultaneously accessed.
It is a further object of the invention to provide a dual band antenna device where either of the two bands can be operated singularly and interchangeably.
Additional objects and features of the invention will be understood from the following description and claims and the accompanying drawings.